1. Technical Field
The invention relates to machine tool control and, more particularly, to a computerized numerical control machine tool and an acceleration/deceleration control method thereof.
2. Description of Related Art
Machine tools have recently begun making use of computerized numerical control technology. The computerized numerical control (CNC) machine tool uses a CNC system to combine movement of the machine tool, and direct the machine tool to control movement of a workpiece. Current demands on the machine tool system include increased functionality, reduced volume of the computer and driving equipment, and improved accuracy of calculation. Promotion of acceleration/deceleration control technology is thus important.
Referring to FIG. 7, a CNC machine tool 1 includes an input unit 11, a transport unit 12, and a drive unit 13. The transport unit 12 is coupled between the input unit 11 and the drive unit 13. The input unit 11 receives a data signal D1 and converts it into a coding signal D2, a velocity signal, as shown in FIG. 8A. The transport unit 12 includes a first filter 121, a second filter 122 and a third filter 123, connected in series. The filters 121, 122, 123 have a plurality of weight values K0˜K3n−1 and a plurality of registers R1˜R9, as shown in FIG. 8B, with the weight values K0˜K3n−1 fixed, and the number of registers R1˜R9 and total weight values K0˜K3n−1 corresponding to an acceleration/deceleration time T1 of the CNC machine tool 1.
The transport unit 12 using the first filter 121, the second filter 122, and the third filter 123, converts the coding signal D2 into a plurality of acceleration/deceleration signals D3, as shown in FIG. 8C. The drive unit 13 controls rotation speed and direction of a motor 14 of machine tool 1, according to each acceleration/deceleration signal D3.
As mentioned, in movement of the machine tool 1, a value of the coding signal D2 is set at 30 units, as shown in FIG. 8A, and the weight values K0˜K3n−1 are set 1 unit, as shown in FIG. 8B. The filters 121, 122, 123 have three registers respectively, and acceleration/deceleration time T1 is set at 3 units.
Generally, for average movement of the acceleration/deceleration control, after the first filter 121 receives the coding signal D2, it calculates and totals the corresponding weight values K0˜K3n−1 to acquire a first velocity signal V1 for acceleration/deceleration time unit, input into the second filter 122. The second filter 122 and the third filter 123 respectively receive first velocity signal V1 and second velocity signal V2 by the movement average method. Accordingly, the CNC machine tool 1 uses the movement average method three times to convert the coding signal D2 to the acceleration/deceleration signal D3, as shown in FIG. 8C.
However, in the movement average method, CNC machine tool 1 requires one pass to set the acceleration/deceleration time to T1, as shown in FIG. 9. Curves A, B, and C are velocity curves from 1st, 2nd, and 3rd passes of the movement average method, such that CNC machine tool 1 requires three full orders of acceleration/deceleration time T1 to achieve stability and is unable to change the shape of the velocity curves according to manufacturing conditions. As such, velocity curves utilizing the movement average method three times are resultingly clock-shaped curves, as shown in FIG. 8C and FIG. 9. In addition, the movement average method of the CNC machine tool 1 causes the motor to experience corner error, and a curve in the E portion to peak sharply, as shown in FIG. 10. Further, the acceleration distance of the motor 14 is too short to accelerate to a maximum speed, which generates a tracking error.